Molded concrete products or masonry units for use in landscaping and design have seen increased popularity with the rise in personal home renovation and improvements. The production of these concrete masonry units is accomplished using different mold assemblies to shape and form different masonry units for objectives. For example, many masonry units are used to create decorative walls and borders in landscaping projects whereas other masonry units serve as interlocking members to create interesting walkways and paths for both interior and exterior design.
The mold assemblies, which form the different types of masonry units, typically include a tamperhead component and a mold, which are driven by a special machine. A typical machine and mold assembly are typically operated under intense conditions such that the mold assembly is cycled approximately every eight to fifteen seconds, producing approximately 25-30 masonry units per cycle. Also, the machines are often run continuously, only stopping to change mold assemblies or make repairs. Although the molds may be changed more or less frequently, the machines are typically stopped two or three times a day to change the molds. Although a skilled technician may be capable of removing a mold assembly and installing a new mold assembly in the machine in approximately 30 minutes, typical mold assembly installations require significantly more time due to the need for accurate aligning of the tamperhead and the mold and calibrating the machine.
Driven by the production machinery, the tamperhead and the mold assembly function together to form and compact the concrete units in the steel cavities of the mold assembly, which form the shape and size of masonry units. After a medium, such as concrete, is poured into the mold cavities, the tamperhead specifically functions to compact the concrete in the mold cavities and then strip the individual units from the mold cavities. To accomplish this, the tamperhead is includes an upper head structure with pairs of stripper shoes and plunger assemblies.
The stripper shoes are custom designed to match with the mold cavities and fit within the inner walls of the mold cavities with only a minimal clearance. Depending on the type and size of product being manufactured, this clearance may range from about 0.2 mm to about 1.5 mm per side. If the clearance is too small, the shoe will rub against the cavity wall inducing stress in the mold and production machinery as well as premature wear. If the clearance is too big, concrete will protrude between shoe and cavity walls, forming “burrs” on top of the product which, at best, detracts from its aesthetic appeal and, at worst, creates installation problems in the field.
The stripper shoes are attached to the upper head structure by structural members referred to as the plunger assemblies. The plunger assemblies attach, typically by welding, the stripper shoes to the upper head structure in a pattern that corresponds to the pattern of mold cavities in the mold. Fabrication of the plunger assemblies traditionally includes two pieces: the backup plate and the plunger.
The plunger is commonly made of rigid length of material such as steel tubing having various cross-sectional shapes capable of providing the structural load path to compress the concrete and strip the formed concrete product from the mold. These cross-sectional shapes may be round, square, rectangle, angle, I-shaped, etc. Further, the plunger may be either solid or hollow.
Traditionally, the backup plate is welded to the plunger after the plunger has been welded to the upper head structure. The backup plate includes holes to facilitate fastening of the stripper shoe and, like with the molds and the stripper shoes, the backup plates are custom fabricated to match the stripper shoes of a specific type of masonry product.
Unfortunately, the welded construction of the two-piece plunger assembly is difficult to fabricate, susceptible to failure, and requires custom redesign for every type of masonry unit. The two-piece welded plunger assembly is costly and time consuming because each plunger assembly is custom designed to provide attachment holes for the fastening of the stripper shoe to the plunger assembly. Additionally, the weld joint between the backup plate to the plunger requires precise welding to ensure correct alignment and functionality between the stripper shoes and the mold cavities. Unfortunately, such precision welding often requires specially trained personnel and additional time and effort in preparing the components before welding.
Previous attempts to attach the stripper shoe directly to the plunger through welding have failed because of welding induced warping of the stripper shoes and the like. Furthermore, the need to precisely align the stripper shoe with the mold cavities traditionally includes tightening the fasteners between the stripper shoes and the backup plates while the stripper shoes are inserted into and aligned with the mold cavities. Additionally, the need to replace broken or damages stripper shoes without replacing the entire tamperhead has made directly welding the stripper shoes to the plunger ineffective.
Additionally, the two-piece fabrication includes a weld joint between the backup plate and the plunger, which is susceptible to failure and material fatigue. During masonry production, the mold is shaken or vibrated to compact the concrete in the molds. This vibration has been shown to induce fatigue and stress failures in the plungers and especially in the weld joints of the plunger assemblies. As a consequence, the backup plate introduces an additional weld joint which is more susceptible to failure from impact stresses or material fatigue than fastening joints, such as the joint between the between the stripper shoe and the backup plate.
Although the stripper shoes and the mold cavities must be custom designed for each type of masonry unit, the use of a custom fabricated plunger assembly for each product type is time consuming and costly. The backup plate is custom fabricated to match the bolt pattern of the stripper shoe before the backup plate is welded to the plunger. Although typically not necessary, the plunger may also need to be custom fabricated or formed from non-standard tubing to accommodate unique stripper shoe designs.
Therefore, there exists a need for a tamperhead employing a universal plunger assembly that reduces the need for custom fabrication of backup plates or plunger elements for different masonry units or product types. There also exists a need to reduce the number weld joints that are susceptible to failure between the stripper shoe and the upper head structure.